Arrangement for full-duplex data transmission over two-wire circuits

Abstract

An arrangement for full-duplex data transmission over a two-wire circuit (1) comprises a transmit channel (2) connected to a baseband data transmitter (6) and including a smearing filter (18), a receive channel (3) connected to a baseband data receiver (9) and including a complementary smearing filter (19), a hybrid junction (4), an echo canceller (14) with an adaptive filter (15) and an adjusting circuit (16), and a combining circuit (17) inserted in the receive channel (3). Despite the application of the smearing filters (18, 19) the complexity of the echo canceller (14) is not increased as the arrangement comprises first and second delay means (20, 21) with a delay (D) corresponding to the signal delay of the cascade connection of the smearing filters (18, 19), the first delay means (20) having been inserted in a first signal path from the output of data transmitter (6) to the adjusting circuit (16) and the second delay means (21) having been inserted in a second signal path from the output of data transmitter (6) via the adaptive filter (15) and the combining circuit (17) to a point (P) in the receive channel (3) where the residual signal to be applied to the adjusting circuit (16) is tapped, and the complementary smearing filter (19) in the receive channel (3) has been inserted between the hybrid junction (4) and the tapping point (P) for the residual signal.

What is claimed is: 
     
       1. An arrangement for full-duplex data transmission over a two-wire circuit, said arrangement comprising: a. a one-way transmit channel having an input for coupling with a baseband data transmitter and including a smearing filter;   b. a one-way receive channel having an output for coupling with a baseband data receiver;   c. a hybrid junction for interconnecting the transmit and receive channels and the two-wire circuit;   d. an echo canceller comprising i. an adaptive filter with adjustable filter coefficients for generating an approximated echo signal from signals in the transmit channel; and   ii. an adjusting circuit for adjusting the filter coefficients, in response to signals in the transmit channel and in response to a residual signal in the receive channel, so as to minimize a predetermined function of the residual signal, said adjusting circuit being coupled with a tapping point in said receive channel so as to receive the residual signal; and     e. a combining circuit in the receive channel for differentially combining the approximated echo signal with incoming signals from the receive channel to generate the residual signal;   f. first delay means in a first signal path which extends from an output of the data transmitter to the adjusting circuit;   g. a complementary smearing filter disposed within the receive channel between the hybrid junction and said tapping point;   h. second delay means in a second signal path which extends from the output of the data transmitter via the adaptive filter and the combining circuit to said tapping point, the first and second delay means creating a delay in the approximated echo signal so as to substantially compensate for a signal delay resulting from the cascade of the smearing filter and the complementary smearing filter; and whereby the complexity of the echo canceller is not affected by the presence of the smearing and complementary smearing filters.     
     
     
       2. An arrangement as claimed in claim 1 wherein the smearing filter in the transmit channel is a time-discrete transversal filter with a shift register connected to the data transmitter output which shaft register likewise forms part of the first delay means. 
     
     
       3. An arrangement as claimed in claim 1 wherein the second delay means is between the adaptive filter and the combining circuit, the second delay means comprising a cascade of a second smearing filter and a second complementary smearing filter, having respective impulse responses corresponding to the impulse responses of the smearing filter in the transmit channel and the complementary smearing filter in the receive channel. 
     
     
       4. An arrangement as claimed in claim 1 wherein the second delay means is between the adaptive filter and said tapping point for the residual signal, the second delay means including: (a) a second smearing filter between the adaptive filter and the combining circuit, the impulse response of which second smearing filter corresponds to the impulse response of the smearing filter in the transmit channel; and   (b) the complementary smearing filter in the receive channel being coupled between the combining circuit and said tapping point for the residual signal.   
     
     
       5. An arrangement as claimed in claim 4 further comprising, for passband data signal transmission: (a) a first modulator in the transmit channel in cascade with the smearing filter;   (b) a second modulator corresponding to the first modulator in cascade with the smearing filter in the second signal path between the adaptive filter and the combining circuit; and   (c) a demodulator associated with the first and the second modulators in the receive channel in cascade with the complementary smearing filter and after the combining circuit.   
     
     
       6. An arrangement for full-duplex data transmission over two-wire circuit, said arrangement comprising: a. a one-way transmit channel having an input for coupling with a baseband data transmitter and including a smearing filter;   b. a one-way receive channel having an output for coupling with a baseband data receiver;   c. a hybrid junction for interconnecting the transmit and receive channels and the two-wire circuit;   d. an echo canceller comprising: i. an adaptive filter with adjustable filter coefficients for generating an approximated echo signal from signals in the transmit channel; and   ii. an adjusting circuit for adjusting the filter coefficients, in response to signals in the transmit channel and in response to a residual signal in the receive channel, so as to minimize a predetermined function of the residual signal, said adjusting circuit being coupled with a tapping point in said receive channel so as to receive the residual signal; and     e. a combining circuit in the receive channel for differentially combining the approximated echo signal with incoming signals from the receive channel to generate the residual signal;   f. a complementary smearing filter in said receive channel between the hybrid junction and said tapping point; and   g. delay means between an output of the data transmitter and the echo canceller, the delay means creating a delay in the approximated echo signal so as to substantially compensate for a signal delay resulting from the cascade of the smearing filter and the complementary smearing filter; whereby the complexity of the echo canceller is not affected by the presence of the smearing and complementary smearing filters.     
     
     
       7. An arrangement as claimed in claim 6, further comprising, for passband data signal transmission: (a) a first modulator in the transmit channel in cascade with the smearing filter;   (b) a second modulator corresponding to the first modulator between the adaptive filter and the combining circuit; and   (c) a demodulator associated with the first and the second modulators in the receive channel after the combining circuit.   
     
     
       8. The arrangement of claim 6 wherein the smearing filter in the transmit channel is a time-discrete transversal filter with a shift register connected to the data transmitter output which shift register likewise forms part of the delay means.